This invention relates generally to mechanical thermostats and, more particularly, to mounting a bimetal coil in a mechanical thermostat.
Mechanical thermostats typically utilize a bi-metal coil having an inner end secured to a fixed point and an outer end configured to move as the coil winds and unwinds in response to temperature changes. Movement of the bi-metal coil operates a contact in an electrical switch for operating the heating and/or cooling system that the thermostat controls. It is cost-effective to secure the coil by mounting it on a pin that also serves as an electrical connection for a heat anticipator circuit. In electrically isolated mercury switch thermostats, the bi-metal coil can be spot-welded to the pin. However, in snap-action thermostats in which a conductive pin is used to mount both the coil and the anticipator circuit, it is necessary to electrically isolate the contact on the bimetal coil from the pin and anticipator circuit, and so other techniques must be used to secure the contact to the bi-metal coil
In at least one known thermostat, the bi-metal coil is perma-bonded to the pin, making it somewhat difficult, however, to calibrate the thermostat. In another thermostat, a conductive eyelet is placed inside the bi-metal. The eyelet then is placed over the pin, placed in a press, and crimped. The contact then is isolated from the conductive pin at a point where contact is attached to the bi-metal coil. Relative to other methods, these techniques involve more parts, greater fabrication cost and a more expensive contact assembly mounted to the thermostat base.
The present invention relates to an improved mounting for bi-metal coils and to thermostats with improved mounting of bi-metal coils. Generally, the thermostat of this invention comprises a base; a conductive shaft extending from the base; and heat anticipator circuit mounted on, and electrically connected to, the conductive shaft. In accordance with the principles of this invention, an electrically insulative member is mounted on the conductive shaft between the base and the anticipator circuit. A temperature-responsive element, such as a bi-metal coil, is mounted on the electrically insulative member electrically isolated from the conductive shaft and anticipator circuit. The element carries a conductive switch member.
The insulative member preferably has a bore therethrough configured to engage the shaft and resist rotation. For example, at least a portion of the shaft and a portion of the bore through the insulative member have mating configurations to resist relative rotation. The insulative member preferably also has an external surface adapted to engage the end of the coil and resist rotation of the coil. For example, the insulative member can have a plurality of longitudinally extending ridges and valleys on the surface to engage the end of the coil and resist relative rotation.
In the preferred embodiment, the insulative member has a flange adjacent one end of the insulative member. The insulative member preferably also has a resilient tab having a barb for engaging and retaining the coil thereon. The resilient tabs can be formed between two generally longitudinally extending slots, and the barb projects radially outwardly from the distal end of the tab, having a sloped face on one side for resiliently deflecting the tab when the coil is urged over the tab, and an oppositely facing flat shoulder for engaging and retaining the coil on the insulating member.
Thus the invention allows the inner end of a bi-metal coil to be secured easily in a thermostat, thus eliminating a need for more expensive mounting methods, costly insulating parts, and reducing labor costs. The apparatus also simplifies calibration while reducing costs of assembly and materials.